Movement Is A Joint Effort: A Look At Synovial Joints

Much of our range of motion capabilities and limitations can be attributed to our joints. (Not the type that can make it difficult to move off the couch, although those can limit your motion too.) While we all contain essentially the same joints in our bodies, their shapes can differ slightly, resulting in different ranges of motion among individuals.

We Come In All Different Shapes: The 6 Synovial Joints

There are six main types of synovial joints in the human body. Each type has a unique design to allow for a variety of movements while restricting others.

  • Hinge Joints: these joints allow for flexion and extension in a single plane, similar to the hinges of a door. Ex: the elbow and knee only move forward and back (although the knee has limited rotation when bent, when straightened there is no rotation in the knee)
  • Ball and Socket Joints: these joints allow for maximum movement in all directions and are located where our axial skeleton meets our appendicular skeleton. Ex: the shoulder and the hips. The hip is a deeper joint to allow for more stability while the shoulder is shallower to allow for a higher range of motion.
  • Ellipsoid Joints: similar to the ball and socket joint except there is little to no rotation. Ex: the wrist can move in all directions except it can’t rotate. (Hold your forearm steady and try waving side to side, the wrist will barely move. That waving rotation comes from the radius twisting over the ulna.)
  • Pivot Joints: allow for rotation around a long axis. Hold your upper arm steady and flip your palm over and back (supination and pronation). When your palm faces up the radius is on the outside of your forearm and runs to the thumb. As the palm flips over the radius rotates over top the ulna, bringing the thumb to the inside of the forearm. This rotation takes place at the radial-ulnar joint by the elbow.
  • Saddle Joints: like its name the saddle joint resembles a horses’ saddle with a concave valley, into which a convex bone inserts (like a rider’s legs hanging on the side of the saddle). The joint at the base of the thumb is a highly articulate saddle joint. These joints allow for flexion & extension, abduction & adduction, circumduction, and very limited rotation (because the ‘legs’ and ‘saddle’ hit against one another).
  • Gliding Joint/Planar Joints: planar joints involve two flat-like surfaces gliding overtop one another. These joints usually come in groups like the carpals in the hand and the tarsals in the foot. These joints tend to have little movement, only being able to glide over one another and rotate.

Our bodies are intelligently designed and we should always strive to use our bodies accordingly. For example, we should never try to rotate strongly at the knee joint since it is a hinge joint and allows for minimal rotation. Many people cause serious injuries to their knees trying to come into lotus pose when their hips are not open enough. We will explore this in much greater detail in upcoming posts.

The Joint Capsule and Synovial Fluid

The outer layer surrounding a joint is referred to as the joint capsule. The joint capsule contains fibrous tissue which provides both strength and stability for the joint. Our joints also contain cartilage, an amazing substance that is actually up to 8x more slippery than ice. Cartilage can also easily soak up and push out fluid, similar to a sponge. Cartilage also stores our synovial fluid. Synovial fluid lubricates our joints to reduce friction and helps to absorb shock, protecting our joints from harm.

Structure of synovial joints.
The structure of a typical synovial joint

Joint Issues

Osteoarthritis: this condition is the most common type of joint pain (especially among older people) and results from the degeneration of cartilage within the joint. This lack of cartilage causes the bones to rub against one another, leading to pain and stiffness.

Rheumatoid Arthritis: this type of arthritis is due to a faulty immune system and causes chronic inflammation in the joints. It is particularly common in the hands.

Rheumatoid arthritis in the joints.
An x-ray of someone with rheumatoid arthritis.

Bursitis: bursitis refers to an inflammation of the bursa. Bursa are little sacs filled with synovial fluid that are strategically placed throughout the body to act as cushions, particularly where muscles and tendons slide across bones. There are over 150 bursa in the body, but the most common areas of bursitis are in the shoulder, elbow, and hip.

Concluding Thoughts

Our joints literally hold space that allows for us to move. Without this space we would be under constant friction, grinding our bones down to nothing. Sometimes in our lives it is important to create some space for ourselves, take a step back, and enjoy our freedom.

Enjoy the freedom within your body. Run, dance, do your yoga, explore the range of motion in your body and accept its limitations. Try not to push yourself beyond your natural range of motion or stretch yourself too thin physically and emotionally. If we work with the natural designs of our bodies we can use this space to accomplish incredible things!

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